In recent memory hard disk drives, there is a demand for decreasing a flying height of a magnetic head so as to enhance a recording density, thereby reducing a unit recording area, for the purpose of achieving a high capacity and a small diameter. In connection with this, even in a process of producing a hard disk, the surface quality such as cleanliness required of a polished surface obtained by polishing an object to be polished is increasing.
The process of producing a hard disk includes a substrate formation step and a media step. In the substrate formation step, a substrate to be polished is subjected to a polishing treatment and a cleaning treatment in this order a plurality of times, whereby a substrate for a hard disk is produced. In the media step, small unevenness is provided to at least one of the principal surfaces of the substrate for a hard disk by polishing as required (texture step), and then the substrate is cleaned (cleaning step) and subsequently a magnetic layer is formed on at least one of the principal surfaces of the substrate (magnetic layer formation step).
In a case where the detergent composition contains a surfactant, a nonionic surfactant is used favorably from the viewpoint of cleaning property (see Patent documents 1-3). Patent document 1 discloses, as a detergent composition containing a nonionic surfactant and having a high cleaning property, an alkaline detergent composition containing not only a nonionic surfactant but a chelating agent and an anionic surfactant.